Home Run Hitting in Statcast Era

Introduction

• There has been remarkable changes in home run hitting during the Statcast period 2015-2025

• What variables influence home runs?

• We will focus on two reasons – batter behavior and ball construction

Data

• Focus on the balls in play

• I have data on all balls in play for all Statcast seasons

• Home run rate is \[ HR \, \,Rate = 100 \, \frac{HR}{BIP} \]

Balls in Play (BIP) and Home Runs (HR) by Season:

In-Play Home Run Rates

Process of Hitting Home Run

• Hit the ball well (hard and at right angle)
• Given that the ball is hit well, the ball has to leave the park

What is a Launch Angle?

Launch Angle measures the vertical angle, in degrees, at which the ball leaves a player’s bat after being hit.

• Ground ball: Lower than 10 degrees
• Line drive: 10-25 degrees
• Fly ball: 25-50 degrees
• Pop up: Higher than 50 degrees

What is Exit Velocity?

• Exit Velocity measures the speed of the baseball as it comes off the bat, immediately after a batter makes contact. This is tracked for all Batted Ball Events – outs, hits and errors.

• Attaining a high Exit Velocity is one of a hitter’s primary goals. A hard-hit ball won’t always have a positive result, but the defense has less time to react, so the batter’s chances of reaching base are higher.

Where is launch space where home runs are hit?

Focus on Two Rates

• Red Rate - the rate of balls in play in the RED region

• HR Rate - among all the balls in the RED region, what percentage are home runs?

• The Red Rate tells us about player behavior, the HR rate tells us about the ball (its carry properties)

HR Rate is Product of Two Rates

\[ \begin{align} HR \, Rate &= \frac{HR}{BIP} \\ \\ &= \frac{RED}{BIP} \times \frac{HR}{RED} \\ \\ &= P(RED) \times P(HR | RED) \end{align} \]

• \(P(RED)\) measures batter behavior

• \(P(HR | RED\) measures ball properties

Add to Table

In-Play Red Rates

What have we learned?

• Players are getting bigger and stronger
• They work on hitting balls on “HR friendly” launch angles
• So there has been a steady increase in RED rates

Home Run Rates in Red Region

What have we learned?

• The increase on home run rates depends on more than the players
• The changes in the RED HR rates reflects properties of the ball
• Some seasons, the ball is lively
• Recently, the ball has been relatively dead
• This impacts records like Aaron Judge’s 62 HR in 2022

Does MLB Care?

• During the big increase in HR hitting, MLB created a committee to study the issue
• Committee made some recommendations
• I don’t think home run hitting is one of the big issues currently